The invention relates to an apparatus for the generation of tomographic X-ray images having enhanced contrast properties. The radiation of an X-ray source is received by a receiver after having passed the object and is converted by an image converter into electrical image signals original images correspond element-by-element to the X-ray radiation. Signals are conducted by an electronic circuit to an image display device, for example, a monitor. Mechanical means produce a tomographic relative movement between the receiver and the X-ray source during the radiation.
As it is well known, single body layers can be displayed by tomographic methods of X-ray images, the depth and thickness of each body layer being selectable all other body layers are displayed out of focus. Usually, layers parallel to the longitudinal axis of the body (object) are recorded. It is of disadvantage within the known recording processes that the interference of contrasts by shadows of other layers cannot be fully avoided. In other words, layers not belonging to the recordal plane, if the diameter of these shadows is bigger than the movment range of the mechanical system used for the tomographic movement are displayed. Even smaller disturbing shadows are displayed in the form of smudges distorting the real picture, if any part of the contour of the shadow presents a curve similar to that of the tomographic movement. Therefore, the contrast and the resolution of the images produced by the known apparatus are not satisfactory. There have been attempts to avoid these disadvantages by complicated tomographic movements, but the desired success has not been reached. In addition, the known methods suffer from the disadvantage that the X-ray doses is comparatively high. This occurs because, when recording, radiographic radiation rates must be used. These disadvantages also result for the known method of computer tomography, particularly, if a longitudinal section is calculated from a plurality of cross sections by means of computers. A common disadvantage of the computer tomograhpy systems is the relatively high cost. The method of the so-called "indirect tomography" uses images amplifiers in combination with usual tomographic systems in order to amplify the photo intensity of the signals before integration of the images on a film of reduced format. It has been shown that this affords no improvement of the image quality.
U.S. Pat. No. 4,079,417 and the document IEEE TRANSACTIONS ON BIOMEDICAL ENTINEERING (volume BME-26, No. 5, May 1979, pages 253-262) disclose a method for increasing the contrast between image elements laying between a selectable grey value range or, respectively, for contrast increase by flattening of the grey value histogramm. However, these methods are not satisfactory.